Ultrafiltration of polyisoolefin copolymers and polyisoolefin copolymers with reduced oligomer content

Abstract

A method of separating a polyisoolefin elastomer from non-polymeric components in an organic solvent involves ultrafiltration of a solution of the polyisoolefin elastomer and non-polymeric components in an organic solvent through a semipermeable membrane to substantially retain the polyisoolefin elastomer in a retentate and provide the non-polymeric components in a permeate. Advantageously, stabilizers for the polyisoolefin elastomer are retained in the retentate along with the polyisoolefin elastomer, permeate flux through the membrane is higher as concentration of the polyisoolefin elastomer in the solution increases up to a concentration limit, the separated polyisoolefin elastomer in the retentate has a molecular weight that can be substantially unchanged even when ultrafiltration is conducted at elevated temperature and the amount of polyisoolefin elastomer in the permeate is unmeasurable providing an oligomer-rich permeate uncontaminated by polyisoolefin elastomer. A process for curing a polyisoolefin copolymer involves reducing content of an oligomer to 900 ppm or less in a mixture of the oligomer and the polyisoolefin copolymer to produce an oligomer-depleted mixture, and adding a resin cure system to the oligomer-depleted mixture to cure the polyisoolefin copolymer.

What is claimed is: 
     
       1. A process for curing a polyisoolefin copolymer comprising isobutylene and isoprene units, the process comprising
 reducing a content of an oligomer, the oligomer comprising one or both of a C 13  and a C 21  unsaturated cyclic oligomer, to 900 ppm or less in a mixture of the oligomer and the polyisoolefin copolymer comprising isobutylene and isoprene units to produce an oligomer-depleted mixture, and 
 adding a resin cure system to the oligomer-depleted mixture to cure the polyisoolefin copolymer. 
 
     
     
       2. The process according to  claim 1 , further comprising reducing the content of the oligomer in the mixture by filtering the mixture of the oligomer and the polyisoolefin copolymer in an organic solvent through a semipermeable ultrafiltration membrane. 
     
     
       3. The process according to  claim 2 , wherein the oligomer depleted mixture is a retentate of the filtration. 
     
     
       4. The method according to  claim 3 , further comprising maintaining concentration of the polyisoolefin copolymer in the organic solvent at 2-40 wt. % based on total weight of the mixture. 
     
     
       5. The process according to  claim 3 , wherein the filtering is performed at a temperature of from 30-200° C., optionally 40-130° C., optionally at a pressure in a range of from 2-50 bar. 
     
     
       6. The process according to  claim 3 , wherein:
 the organic solvent comprises one or more stabilizers for the polyisoolefin copolymer, 
 the one or more stabilizers comprise particulate solids insoluble in the organic solvent, non-permeating liquids immiscible in the organic solvent, or a combination thereof, and 
 at least one of the one or more stabilizers is retained in the retentate in an amount of from about 80-100 wt. % based on weight of the original amount of the at least one stabilizer in the organic solvent, optionally about 95-100 wt. %. 
 
     
     
       7. The process according to  claim 6 , wherein the one or more stabilizers comprise an acid scavenger, optionally comprising a metal carboxylate, optionally in the form of a particulate solid, or a metal oxide or hydroxide, optionally comprising calcium stearate or sodium hydroxide, or a mixture of a metal carboxylate and a metal oxide or hydroxide. 
     
     
       8. The process according to  claim 3 , wherein a molecular weight of the polyisoolefin is decreased by less than about 15% during the filtering step. 
     
     
       9. The process according to  claim 3 , wherein the organic solvent comprises hexane, pentane, isohexane, isopentane or any mixture thereof and optionally the mixture comprises about 1-60 wt. % water based on the total weight of the mixture. 
     
     
       10. The process according to  claim 2 , wherein the filtering comprises a crossflow ultrafiltration, optionally a constant volume crossflow ultrafiltration, optionally having a crossflow velocity of the solution across the ultrafiltration membrane in a range of from 0.5-10 m/s. 
     
     
       11. The process according to  claim 10 , further comprising maintaining crossflow velocity (v CF ) of the solution across the ultrafiltration membrane, concentration (y IIR ) of the polyisoolefin copolymer in the solution and permeate flux (J) through the ultrafiltration membrane to satisfy Equation 1: 
       
         
           
             
               
                 
                   
                     α 
                     = 
                     
                       
                         
                           y 
                           IIR 
                         
                         ⁢ 
                         J 
                       
                       
                         v 
                         CF 
                       
                     
                   
                 
                 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                 
               
             
           
         
       
       where α is a unitless quantity greater than 3×10 −7 . 
     
     
       12. The process according to  claim 1 , further comprising reducing the content of the oligomer in the mixture by precipitating the polyisoolefin copolymer from a solution of the mixture in a solvent. 
     
     
       13. The process according to  claim 1 , wherein curing the polyisoolefin copolymer in the oligomer-depleted mixture increases cure state of the polyisoolefin copolymer by at least 8% compared to a cure state of the polyisoolefin copolymer when cured in a mixture having an oligomer content of more than 900 ppm. 
     
     
       14. The process according to  claim 1 , wherein the content of the oligomer in the mixture is reduced to 250 ppm or less. 
     
     
       15. The process according to  claim 1 , wherein the resin cure system includes a halogenated phenol formaldehyde resin. 
     
     
       16. The process according to  claim 15 , wherein the resin cure system includes an activator. 
     
     
       17. The process according to  claim 15 , wherein the resin cure system includes a metal oxide. 
     
     
       18. The process according to  claim 17 , wherein the metal oxide is zinc oxide. 
     
     
       19. The process according to  claim 15 , wherein the resin cure system includes a processing aid. 
     
     
       20. The process according to  claim 19 , wherein the processing aid includes stearic acid. 
     
     
       21. The process according to  claim 15 , wherein the amount of the resin is about 0.2 to about 10 parts by weight, based on the total weight of the polyisoolefin copolymer. 
     
     
       22. The process according to  claim 1 , wherein resin cure system includes a phenol formaldehyde resin. 
     
     
       23. The process according to  claim 22 , wherein the resin cure system includes an activator. 
     
     
       24. The process according to  claim 22 , wherein the resin cure system includes a metal oxide. 
     
     
       25. The process according to  claim 24 , wherein the metal oxide is zinc oxide. 
     
     
       26. The process according to  claim 22 , wherein the resin cure system includes a processing aid. 
     
     
       27. The process according to  claim 26 , wherein the processing aid includes stearic acid. 
     
     
       28. The process according to  claim 22 , wherein the amount of the resin is about 0.2 to about 10 parts by weight, based on the total weight of the polyisoolefin copolymer. 
     
     
       29. The process according to  claim 1 , wherein the resin cure system includes an alkyl phenol formaldehyde derivative.